O'Brien JM, Kingsbury JS. A practical synthesis of 3-acyl cyclobutanones by [2 + 2] annulation. Mechanism and utility of the Zn(II)-catalyzed condensation of α-chloroenamines with electron-deficient alkenes.
J Org Chem 2011;
76:1662-72. [PMID:
21344895 DOI:
10.1021/jo102257k]
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Abstract
New conditions for the conversion of simple tertiary amides to α-chloroenamines and their use in Zn(II)-catalyzed cycloaddition reactions with commercial α,β-unsaturated carbonyl compounds allows rapid, regiocontrolled access to 3-acyl cyclobutanones. Reactions take place at ambient temperature without solvent, giving strained [2 + 2] adducts with all-carbon-substituted quaternary carbon atoms. Ab initio calculations of the putative keteniminium intermediate and studies with styrenyl olefins suggest a dual role for Zn(OTf)(2) during catalysis.
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